Evans Water Engineers | Rural Development

EVANS ENGINEERING

TRECARRELL MILL · TREBULLETT · LAUNCESTON · CORNWALL · UK · PL15 9QE
+44 1566 782285 · www.evans-engineering.co.uk · email sales@evans-engineering.co.uk

Waterpower for rural development

 

The Size of project ranges from as little as 10 watts to over 50 kW for community schemes and even larger mini-hydro schemes are installed by governments to feed national or local grid networks. The important thing to remember is that the organisations and regulations should be appropriate to the scale of the developments. Many countries have made the mistake of over-regulating and requiring even tiny agricultural units to conform to regulations intended for multi-megawatt installations.

Low Voltage systems (12/24 volt DC) may be used directly for battery charging. In other situations a battery charging station can charge batteries at night that have been brought in by villagers who are to far away for a wired connection. Very small units of a few watts can also be used for running low wattage LED lighting or appliances. Domestic power for lighting, hot water and possibly cooking, will produce a 110/220volt supply. This may run a battery charging station or modest distribution network up to half a kilometre from the powerhouse. Commercial mills and agricultural enterprises using mechanical power, but can also provide village lighting at night by engaging a generator.

The electrical systems that are used depends largely on the type of generator used. Brushless generators are favoured on the grounds of low maintenance but are less easy to control or are more expensive than other brushed types. Induction motors can and are used as generators in some countries, but the voltage regulation that is necessary to prevent damage to equipment, is not straightforward for non-technical people. Permanent magnet generators are efficient and reliable but again the voltage regulation is difficult without electronics in the main line or in parallel with the generator output to switch a ballast load in order to keep the speed constant.

Wound field generators offer a good reliable solution but are the most expensive. Where a good electronic voltage regulator is used to control the field, no other controls are usually required. The voltage should stay substantially constant whatever the input speed. If constant frequency is important, other devices can be added but are not essential from the outset.

Mechanical governing systems that operate on the turbine itself or the drive to the generator, are usually more expensive and are difficult to implement but some layouts are possible and it solves most of the other problems.


Commercial, or microhydro systems with outputs from 5 to 50 kW.

These power stations can be regarded as an alternative to a diesel generating plant. They produce a regulated voltage and frequency and are usually set up with the approval or help of a government agency or ministry. They may be ‘stand-alone’, supply a ‘mini-grid’ or be connected into the ‘main grid’ system.

Most plants will at some time have to run in isolation so they will require a governing system and have to provide their own electrical excitation. Induction generators that rely on the grid for excitation and control are simple and useful for supplying the ‘base load’ but are rather inflexible. Remote rural areas often suffer from very poor power-factor and a microhydro plant with an oversized synchronous generator can help improve this situation be supplying the ‘reactive power’ and controlling the line voltage.

Mechanical power for agricultural processing, lighting and pumping

In some countries there exists already, large numbers of water driven grain mills. These may be of vertical or horizontal layout and are usually made of wood and producing less than 5 kW. Typically the efficiency is about ten or fifteen percent, so there is considerable scope for improvement. The new improved mills can offer at least three times the output and simple open turbines, as much as six times the output for the same water flow. These small enterprises have need for power but they may also provide electricity for village lighting, hot water and storage cooking at night when the power is not needed by the mill.

Mechanical Power for raising water for drinking purposes or for micro- irrigation

Other applications need no governing and these include water pumping. Here a large flow of water and a fall as little as 500mm, is used to drive a high pressure pump to lift a small part of the water to a height of several hundred metres. Unlike a hydraulic ram, a turbine/pump unit can be very flexible and is physically much smaller and cheaper than a ram of the same output.

The use of hydropower to aid rural development has great potential given the right climate and topographical features. It can also serve as a training channel through which local people can learn about water, engineering and electricity. Planning the programme as a series of upgrades from improved mill to commercial enterprise and electrification, is likely to be more successful than simply building a power-station that has little or no contact with the community.

At the small commercial level there is considerable scope for village women to manage and develop electricity distribution. Millers may be technical but frequently don’t have the skills or motivation to sell and collect revenue from off-peak electricity generation. Women stand to benefit most from centralised hot water supplies, drying and cooking facilities and can work out the way benefits are shared, while the miller is simply paid an appropriate rate for the electricity he would otherwise not generate.

Programmes that are based purely on the purchase of equipment that is installed like large power stations, is doomed to failure and there are warehouses around the world full of unused and inappropriate equipment. You need strong local organisations for implementation and training. It also helps if there is a clear identifiable economic, social or environmental benefit that the community supports. It has frequently been the case in the past that a village hydro plant only gets connected to those close to the power station or village elders. If the villagers are to help build the project, they must see some return for their efforts. The greater good of saving forests from being used for fuel does not ‘cut much ice’ when you are poor and need to cook for your family.